Vacuum variable capacitor



March 22, 1966 J. E. JENNINGS 3,242,397

VACUUM VARIABLE CAPACITOR Filed Dec. 11, 1961 do [MM/f rr (/E/V/Vl/V65 IN VEN TOR.

United States Patent Oflice 3,242,397 Patented Mar. 22, 1966 3,242,397 VACUUM VARIABLE CAPACITOR Jo Emmett Jennings, San Jose, Calif., assignor to Jennings Radio Manufacturing Corporation, San Jose,

Calif., a corporation of Delaware Filed Dec. 11, 1961, Ser. No. 158,188 13 Claims. (Cl. 317245) My invention relates to vacuum variable capacitor; and one of the objects of my invention is the provision of a vacuumized cylindrical envelope having its cylindrical wall including a bellows structure permitting axial contraction and expansion of the entire envelope to accompany movement of the mobile condenser plates.

Another object of the invention is to provide an envelope comprising a plurality of rigid ceramic rings hermetically connected by metallic expansion joints of bellows type, so that a wide range of expansion and contraction of the envelope is secured with almost negligible flexure at any one fold of the expansion joints, and with'consequent long life of the joints and of the envelope.

Still another object of my invention is the provision of an hermetically tight envelope having oppositely arranged end walls on which condenser plates are rigidly mounted and a cylindrical side wall including expansion joints, so that the condenser plates may be adjusted by controlled movement of an end plate.

Other objects will be brought out in the following description of the invention. I do riot limit myself to the showing made by said description, since I may use variant forms of the invention within the scope of the appended claims.

Wi-th reference to the drawing, the figure is a half sectional view of a capacitor embodying my invention. The scale of the implement described is approximately full slze.

A basic feature of my vacuum variable capacitor is a hermetically sealed con-tractive and expansive cylindrical wall structure, closed at opposite end-s by end plates on the inner faces of which the condenser plates are rigidly secured in interlappin'g arrangement. Varialble adjustment of the plates is obtained by the application of controlled force to the outside of one of the end plates. Preferably the entire envelope is enclosed in aprotective housing, in one end of which a slide bearing is disposed for the shaft which controls movement of one of the end plates.

A particular advantage of my contractive and expansive envelope wall lies in the almost negligible amount of fiexure in each individual fold of the bellows'sections even after many full excursions of the plates. Failure on account of fatigue and breakdown in the folds of the expansion joints is unlikely at any time.

The wall structure 1, comprising the vacuumized envelope of my invention comprises a plurality of ceramic rings 2, metallized on their edges and assembled into a cylindrical wall structure or envelope by brazing a short section 3 of copper bellows between each two adjacent rings. For added stability, the upper end 4 which is a ceramic disk, is brazed to the top ring by an intervening stiff single fold 6 of relatively thick copper, the engaging surfaces of the ceramic having first been metallized.

The lower end of the envelope is closed by an inwardly extending conical shell 7, the radially extending flange 8 of which is brazed to the lowest ceramic ring 2. A downwardly extending tubulation 9 is arranged on the outer surface of the conical shell as shown, for use during exhaustion eat the envelope.

Brazed to the outside of the conical shell at its inner and smaller end, is an outwardly extending sleeve '12, arranged to receive the end 13 of the copper operating shaft 14, brazed therein.

The shaft has a slide bearing in the replaceable Teflon bearing 16, threaded into the hub 17 of the dielectric end plate 18. The free end 19 of the shaft is reduced in diameter and threaded to receive a cylindrical nut 2 1, forming a stop to limit inward travel of the shaft. A terminal connector 22 is tightened against the stop by the nut 23; and the dielectric end 24 of the conventional or other operator is threaded on the shaft end.

For ordinary use, I prefer to protect my ceramic-bellows envelope by fixing it-wi-thin a protective case or housing '26, conveniently molded of nylon, silicon, fibreglass or other dielectric material in a cylindrical cup shape closed at its'ope'n end by the end plate 18. In this construction, the upper end 4 of the vacuumized envelope is seated in a shallow inner recess 27 in the bottom of the cup. Where the housing is to be used, and in a large capacitor, one of the central ceramic rings is formed with a bead 2 8, lying close to but not touching the inside surface "of the housing. The bead insures against lateral movement or the envelope during shipment and use.

The envelope is of course vacuumized, but the protective housing remains at atmospheric pressure, and demay be provided with apertures for the free flow of 'air around the envelope in addition to the vent'opening 29.

A copper stud 30 extends through the bottom of the cup and through the end 4ofthe envelope, spreads out into a fixed mounting plate 31 and acentral axially aligned hollow stud 32. The stud forms an hermetic union with the plate 4, by brazing to the metallized edge of the hole through which it passes; and stud and plate are held securely against the cup bottom by the screw 36 threaded into the stud and carrying "the nut 34 over the intervening washer 3-5. The screw 33 also serves as a terminalfor the connection of my capacitor into 'a circuit.

Extending upwardly from the inner-most end of the conical shell 7, and brazed thereto, in axial alignment with the shaft "14 and stud 30, is an apertured tubular stem 36, conveniently of copper, and brazed at its upper end to the bearing sleeve 37, centralized in the mobile mounting plate 38, parallel to and spaced from the fixed mounting plate 31. A dielectric shaft 39, preferably of sapphire, is secured in the hollow stud 32 and slides in the bearing sleeve 37 to insure and preserve close axial alignment of the mounting plates 31 and 38 and the condenser plates 41 and 42 respectively brazed thereon in interlapping relation.

From the above it will be clear that the condenser plate-s may be inter-lapped to any desired extent by selective movement of the operating shaft 14 and that during such movement the vacuumized envelope is compressed or expanded with but small fiexure of any single bellows fold and complete preservation of the vacuum in the envelope. The multiplicity of operative movements with negligible fatigue of the bellows folds which is thus provided assures a long and almost indefinite operative life for my capacitor, while the enclosing housing gives security against injury from outside sources.

I claim:

1. A variable capacitor including an hermetically sealed envelope comprising:

(a) a cylindrical wall structure including a plurality of spaced dielectric rings and an axially expansible wall section hermetically interposed between at least two adjacent dielectric rings,

(b) a fixed end plate having an opening therein and hermetically connected to and closing one end of the wall structure,

(0) a mobile end plate hermetically connected to and closing the other end of the wall structure to complete an hermetically tight envelope and movable toward and away from the fixed end plate,

(d) a terminal stud mounted on the fixed end plate and extending hermetically through said opening, (e) fixed and mobile series of condenser plates supported on the fixed and mobile end plates respectively, and

(f) an operating shaft secured to the mobile end plate to effect movement of the mobile end plate and the mobile condenser plates toward or away from the fixed series of condenser plates.

2. The combination according to claim 1, in which said series of fixed and mobile condenser plates are cylindrical and concentric, and bearing means are operatively interposed between said fixed and mobile .end plates to maintain the concentric relationship of the cylindrical condenser plates during movement toward or away from each other.

3. The combination according to claim 1, in which said fixed end plate comprises an annular dielectric disc, and said terminal stud hermetically seals the opening therein.

4. The [combination according to claim 1, in which said mobile end plate comprises an inwardly extending truncated conical shell closed at its apex end and sealed adjacent its base end to the wall structure, and said operating shaft is fixed to the apex end 'of the shell.

. 5. The combination according to claim 1, in which said mobile series of condenser plates comprises a plurality of concentric cylindrical shells, a bearing sleeve is concentrically disposed and secured within the innermost of 'said shells, and a dielectric stud shaft fixed in relation to said fixed series of condenser plates is slidably disposed within said bearing sleeve.

6. The combination according to claim 1, in which a housing is provided enclosing the hermetically sealed envelope, said housing including side walls confining at least a portion of the cylindrical wall structure against transverse displacement with respect to the axis thereof.

7. The combination according to claim 6, in which at least one of said dielectric rings is provided with a bead about its outer periphery cooperating with the side walls of the housing to maintain a space between the housing and envelope to enable circulation of a fluid coolant.

8, The combination according to claim 1, in which a housing is provided enclosing the hermetically sealed envelope, said housing including a first end wall fixed to said fixed end plate and a second end wall cooperating with said operating shaft to guide movement of the mobile end plate of the hermetically sealed envelope along the axis thereof.

9. The combination according to claim 8, in which a slide bearing is detachably disposed on said second end wall of the housing to guide movement of the operating shaft therethrough.

10. The combination according to claim 1, in which said axially expansible wall section hermetically interposed between at least two adjacent dielectric rings comprises a metallic bellows having opposite ends hermetically bonded to associated ends of the dielectric rings.

11. The combination according to claim 1, in which one of said dielectric rings lies next adjacent the fixed end plate and an annular U-shaped seal ring is hermetically interposed between said fixed end plate and said dielectric ring.

12.- The combination according to claim 1, in which one of said dielectric rings is hermetically united directly to said mobile end plate.

13. The combination comprising an hermetically sealed envelope containing a variable capacitor, said en-.'

velope being symmetrical about a longitudinal axis and including an axially expansible cylindrical wall section.

means mounted in said housing to effect relative move-. ment of said other end of the envelope to expand or contract the cylindrical wall section of the envelope, thereby varying the capacitance of said variable capacitor, and means interposed between the envelope and the housing to maintain an annular space therebetween.

References Cited by the Examiner UNITED STATES PATENTS JOHN F. BURNS, Primary Examiner.

JOHN P. WILDMAN, Examiner.

3/1960 Glauber 317-245. 2,992,634 7/1961 Peters 12l48 

1. A VARIABLE CAPACITOR INCLUDING AN HERMETICALLY SEALED ENVELOPE COMPRISING: (A) A CYLINDRICAL WALL STRUCTURE INCLUDING A PLURALITY OF SPACED DIELECTRIC RINGS AND AN AXIALLY EXPANSIBLE WALL SECTION HERMETICALLY INTERPOSED BETWEEN AT LEAST TWO ADJACENT DIELECTRIC RINGS, (B) A FIXED END PLATE HAVING AN OPENING THEREIN AND HERMETICALLY CONNECTED TO AND CLOSING ONE END OF THE WALL STRUCTURE, (C) A MOBILE END PLATE HERMETICALLY CONNECTED TO AND CLOSING THE OTHER END OF THE WALL STRUCTURE TO COMPLETE AN HERMETICALLY TIGHT ENVELOPE AND MOVABLE TOWARD AND AWAY FROM THE FIXED END PLATE, (D) A TERMINAL STUD MOUNTED ON THE FIXED END PLATE AND EXTENDING HERMETICALLY THROUGH SAID OPENING, (E) FIXED AND MOBILE SERIES OF CONDENSER PLATES SUPPORTED ON THE FIXED AND MOBILE END PLATES RESPECTIVELY, AND (F) AN OPERATING SHAFT SECURED TO THE MOBILE END PLATE TO EFFECT MOVEMENT OF THE MOBILE END PLATE AND THE MOBILE CONDENSER PLATES TOWARD OR AWAY FROM THE FIXED SERIES OF CONDENSER PLATES. 